Blacklines/Darklines - rear light clusters that do not have the indicator lens as orange. If you look in the UK3 thread, you'll see several cars with these rear light clusters fitted. They look (IMO) much nicer than the standard light cluster.

I keep reading about blacklines, something to do with black lines at the back of the car? Help me out here....

The blacklines are an official BMW alternative rear light cluster. I have them on my car now and I think they look really great on Sapphire Black:

This is the standard cluster on the same colour car:

They are available on ebay or from the dealer - around £130

In terms of the high gloss shadowline, since you are thinking about an m-sport it's worth mentioning that it isn't just for the chrome strip around the windows. It also picks up the door pillars and the area around the wing mirrors - which are matt plastic on SE's. Very nice detail. You can see the gloss finish on these parts in this picture of my car.

This is the SE look:

BTW - thanks to Matt for the pictures especially the one of my car here ... I really like it.